In order to operate a semiconductor integrated circuit at a low voltage, a step-down regulator circuit is mounted on the semiconductor integrated circuit and the semiconductor integrated circuit is operated at a voltage lower than a power supply voltage. A low dropout (LDO) series regulator is used as a step-down regulator circuit.
However, when the difference between a power supply voltage and an output voltage of an LDO series regulator is large, the voltage difference causes heating losses. Accordingly, a charge pump circuit that reduces a power supply voltage to ½ is connected to the LDO series regulator, an output voltage of the charge pump circuit becoming the input voltage to the LDO series regulator. In this way, a difference between the input voltage and an output voltage of the LDO series regulator decreases, and losses from the LDO series regulator decrease.
The charge pump circuit includes a first switch connected between a power terminal and one end of a capacitor, a second switch connected between one end of the capacitor and an output terminal, a third switch between the output terminal and the other end of the capacitor, and a fourth switch connected between the other end of the capacitor and a ground terminal.
In the charge pump circuit, switching is repeatedly performed between a first state in which the first and third switches are turned on and the second and fourth switches are turned off and a second state in which the first and third switches are turned off and the second and fourth switches are turned on.
At the time of the switching, the output terminal and the ground terminal are short-circuited when the third and fourth switches are simultaneously turned on. Accordingly, in order to prevent the short-circuit, a non-overlap switching method is generally performed in the switching of the switches.
In the non-overlap switching method, however, a state in which all of the switches are turned off occurs, during which supply of a current to the output terminal is interrupted, and thus there is a problem that an output potential of the charge pump circuit is abruptly dropped. As a result, a relatively large variation in the output voltage, a so-called ripple, occurs in the LDO series regulator.